[ARM] S3C64XX: Initial support for DVFS

This patch provides initial support for CPU frequency scaling on the
Samsung S3C ARM processors. Currently only S3C6410 processors are
supported, though addition of another data table with supported clock
rates should be sufficient to enable support for further CPUs.

Use the regulator framework to provide optional support for DVFS in
the S3C cpufreq driver. When a software controllable regulator is
configured the driver will use it to lower the supply voltage when
running at a lower frequency, giving improved power savings.

When regulator support is disabled or no regulator can be obtained
for VDDARM the driver will fall back to scaling only the frequency.
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>

arch/arm/Kconfig

@@ -1241,7 +1241,7 @@ endmenu
 
 menu "CPU Power Management"
 
-if (ARCH_SA1100 || ARCH_INTEGRATOR || ARCH_OMAP || ARCH_PXA)
+if (ARCH_SA1100 || ARCH_INTEGRATOR || ARCH_OMAP || ARCH_PXA || ARCH_S3C64XX)
 
 source "drivers/cpufreq/Kconfig"
 
@@ -1272,6 +1272,10 @@ config CPU_FREQ_PXA
 	default y
 	select CPU_FREQ_DEFAULT_GOV_USERSPACE
 
+config CPU_FREQ_S3C64XX
+	bool "CPUfreq support for Samsung S3C64XX CPUs"
+	depends on CPU_FREQ && CPU_S3C6410
+
 endif
 
 source "drivers/cpuidle/Kconfig"

arch/arm/plat-s3c64xx/Makefile

@@ -23,6 +23,7 @@ obj-y				+= gpiolib.o
 
 obj-$(CONFIG_CPU_S3C6400_INIT)	+= s3c6400-init.o
 obj-$(CONFIG_CPU_S3C6400_CLOCK)	+= s3c6400-clock.o
+obj-$(CONFIG_CPU_FREQ_S3C64XX)  += cpufreq.o
 
 # PM support
 

arch/arm/plat-s3c64xx/cpufreq.c

+/* linux/arch/arm/plat-s3c64xx/cpufreq.c
+ *
+ * Copyright 2009 Wolfson Microelectronics plc
+ *
+ * S3C64xx CPUfreq Support
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/init.h>
+#include <linux/cpufreq.h>
+#include <linux/clk.h>
+#include <linux/err.h>
+#include <linux/regulator/consumer.h>
+
+static struct clk *armclk;
+static struct regulator *vddarm;
+
+#ifdef CONFIG_CPU_S3C6410
+struct s3c64xx_dvfs {
+	unsigned int vddarm_min;
+	unsigned int vddarm_max;
+};
+
+static struct s3c64xx_dvfs s3c64xx_dvfs_table[] = {
+	[0] = { 1000000, 1000000 },
+	[1] = { 1000000, 1050000 },
+	[2] = { 1050000, 1100000 },
+	[3] = { 1050000, 1150000 },
+	[4] = { 1250000, 1350000 },
+};
+
+static struct cpufreq_frequency_table s3c64xx_freq_table[] = {
+	{ 0,  66000 },
+	{ 0, 133000 },
+	{ 1, 222000 },
+	{ 1, 266000 },
+	{ 2, 333000 },
+	{ 2, 400000 },
+	{ 3, 532000 },
+	{ 3, 533000 },
+	{ 4, 667000 },
+	{ 0, CPUFREQ_TABLE_END },
+};
+#endif
+
+static int s3c64xx_cpufreq_verify_speed(struct cpufreq_policy *policy)
+{
+	if (policy->cpu != 0)
+		return -EINVAL;
+
+	return cpufreq_frequency_table_verify(policy, s3c64xx_freq_table);
+}
+
+static unsigned int s3c64xx_cpufreq_get_speed(unsigned int cpu)
+{
+	if (cpu != 0)
+		return 0;
+
+	return clk_get_rate(armclk) / 1000;
+}
+
+static int s3c64xx_cpufreq_set_target(struct cpufreq_policy *policy,
+				      unsigned int target_freq,
+				      unsigned int relation)
+{
+	int ret;
+	unsigned int i;
+	struct cpufreq_freqs freqs;
+	struct s3c64xx_dvfs *dvfs;
+
+	ret = cpufreq_frequency_table_target(policy, s3c64xx_freq_table,
+					     target_freq, relation, &i);
+	if (ret != 0)
+		return ret;
+
+	freqs.cpu = 0;
+	freqs.old = clk_get_rate(armclk) / 1000;
+	freqs.new = s3c64xx_freq_table[i].frequency;
+	freqs.flags = 0;
+	dvfs = &s3c64xx_dvfs_table[s3c64xx_freq_table[i].index];
+
+	if (freqs.old == freqs.new)
+		return 0;
+
+	pr_debug("cpufreq: Transition %d-%dkHz\n", freqs.old, freqs.new);
+
+	cpufreq_notify_transition(&freqs, CPUFREQ_PRECHANGE);
+
+#ifdef CONFIG_REGULATOR
+	if (vddarm && freqs.new > freqs.old) {
+		ret = regulator_set_voltage(vddarm,
+					    dvfs->vddarm_min,
+					    dvfs->vddarm_max);
+		if (ret != 0) {
+			pr_err("cpufreq: Failed to set VDDARM for %dkHz: %d\n",
+			       freqs.new, ret);
+			goto err;
+		}
+	}
+#endif
+
+	ret = clk_set_rate(armclk, freqs.new * 1000);
+	if (ret < 0) {
+		pr_err("cpufreq: Failed to set rate %dkHz: %d\n",
+		       freqs.new, ret);
+		goto err;
+	}
+
+#ifdef CONFIG_REGULATOR
+	if (vddarm && freqs.new < freqs.old) {
+		ret = regulator_set_voltage(vddarm,
+					    dvfs->vddarm_min,
+					    dvfs->vddarm_max);
+		if (ret != 0) {
+			pr_err("cpufreq: Failed to set VDDARM for %dkHz: %d\n",
+			       freqs.new, ret);
+			goto err_clk;
+		}
+	}
+#endif
+
+	cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);
+
+	pr_debug("cpufreq: Set actual frequency %lukHz\n",
+		 clk_get_rate(armclk) / 1000);
+
+	return 0;
+
+err_clk:
+	if (clk_set_rate(armclk, freqs.old * 1000) < 0)
+		pr_err("Failed to restore original clock rate\n");
+err:
+	cpufreq_notify_transition(&freqs, CPUFREQ_POSTCHANGE);
+
+	return ret;
+}
+
+#ifdef CONFIG_REGULATOR
+static void __init s3c64xx_cpufreq_constrain_voltages(void)
+{
+	int count, v, i, found;
+	struct cpufreq_frequency_table *freq;
+	struct s3c64xx_dvfs *dvfs;
+
+	count = regulator_count_voltages(vddarm);
+	if (count < 0) {
+		pr_err("cpufreq: Unable to check supported voltages\n");
+		return;
+	}
+
+	freq = s3c64xx_freq_table;
+	while (freq->frequency != CPUFREQ_TABLE_END) {
+		if (freq->frequency == CPUFREQ_ENTRY_INVALID)
+			continue;
+
+		dvfs = &s3c64xx_dvfs_table[freq->index];
+		found = 0;
+
+		for (i = 0; i < count; i++) {
+			v = regulator_list_voltage(vddarm, i);
+			if (v >= dvfs->vddarm_min && v <= dvfs->vddarm_max)
+				found = 1;
+		}
+
+		if (!found) {
+			pr_debug("cpufreq: %dkHz unsupported by regulator\n",
+				 freq->frequency);
+			freq->frequency = CPUFREQ_ENTRY_INVALID;
+		}
+
+		freq++;
+	}
+}
+#endif
+
+static int __init s3c64xx_cpufreq_driver_init(struct cpufreq_policy *policy)
+{
+	int ret;
+	struct cpufreq_frequency_table *freq;
+
+	if (policy->cpu != 0)
+		return -EINVAL;
+
+	if (s3c64xx_freq_table == NULL) {
+		pr_err("cpufreq: No frequency information for this CPU\n");
+		return -ENODEV;
+	}
+
+	armclk = clk_get(NULL, "armclk");
+	if (IS_ERR(armclk)) {
+		pr_err("cpufreq: Unable to obtain ARMCLK: %ld\n",
+		       PTR_ERR(armclk));
+		return PTR_ERR(armclk);
+	}
+
+#ifdef CONFIG_REGULATOR
+	vddarm = regulator_get(NULL, "vddarm");
+	if (IS_ERR(vddarm)) {
+		ret = PTR_ERR(vddarm);
+		pr_err("cpufreq: Failed to obtain VDDARM: %d\n", ret);
+		pr_err("cpufreq: Only frequency scaling available\n");
+		vddarm = NULL;
+	} else {
+		s3c64xx_cpufreq_constrain_voltages();
+	}
+#endif
+
+	freq = s3c64xx_freq_table;
+	while (freq->frequency != CPUFREQ_TABLE_END) {
+		unsigned long r;
+
+		/* Check for frequencies we can generate */
+		r = clk_round_rate(armclk, freq->frequency * 1000);
+		r /= 1000;
+		if (r != freq->frequency)
+			freq->frequency = CPUFREQ_ENTRY_INVALID;
+
+		/* If we have no regulator then assume startup
+		 * frequency is the maximum we can support. */
+		if (!vddarm && freq->frequency > s3c64xx_cpufreq_get_speed(0))
+			freq->frequency = CPUFREQ_ENTRY_INVALID;
+
+		freq++;
+	}
+
+	policy->cur = clk_get_rate(armclk) / 1000;
+
+	/* Pick a conservative guess in ns: we'll need ~1 I2C/SPI
+	 * write plus clock reprogramming. */
+	policy->cpuinfo.transition_latency = 2 * 1000 * 1000;
+
+	ret = cpufreq_frequency_table_cpuinfo(policy, s3c64xx_freq_table);
+	if (ret != 0) {
+		pr_err("cpufreq: Failed to configure frequency table: %d\n",
+		       ret);
+		regulator_put(vddarm);
+		clk_put(armclk);
+	}
+
+	return ret;
+}
+
+static struct cpufreq_driver s3c64xx_cpufreq_driver = {
+	.owner		= THIS_MODULE,
+	.flags          = 0,
+	.verify		= s3c64xx_cpufreq_verify_speed,
+	.target		= s3c64xx_cpufreq_set_target,
+	.get		= s3c64xx_cpufreq_get_speed,
+	.init		= s3c64xx_cpufreq_driver_init,
+	.name		= "s3c",
+};
+
+static int __init s3c64xx_cpufreq_init(void)
+{
+	return cpufreq_register_driver(&s3c64xx_cpufreq_driver);
+}
+module_init(s3c64xx_cpufreq_init);